GATE — Environmental Science and Engineering (ES) · India · IITs and IISc on rotation (2026: IIT Guwahati)
Original practice questions written to the published syllabus · not past papersMicroorganisms as the engines of nutrient cycling, wastewater treatment, bioremediation and disease. GATE ES Section 3 examines it from cell structure to Monod kinetics and coliform counts.
In the exams: GATE ES Section 3; UGC NET Environmental Sciences Unit 3; ICAR AICE subject 71 Units 4–5 (bioremediation, composting)
GATE — Environmental Science and Engineering, Section 3 (environmental microbiology)
Cell structure and classification, metabolism and ATP yields, fermentation and anaerobic processes, Michaelis–Menten and Monod kinetics, specific growth rate and doubling time, chemostat steady state and washout, disinfection (Ct, log reduction, D-value), nutrient cycling organisms, and MPN and membrane filtration counts, with numerical answer type questions.
How our questions for GATE spread across the units of Environmental Microbiology. Difficulty: 12 easy, 58 medium, 25 hard.
| Control of microorganisms: physical and chemical methods | 9 | |
| Coliform enumeration: MPN and membrane filtration | 9 | |
| Microbial metabolism: glycolysis, TCA cycle, electron transport | 8 | |
| Enzymes and enzyme kinetics | 8 | |
| Batch and continuous culture | 8 | |
| Microorganisms in biogeochemical cycling | 8 | |
| Prokaryotic and eukaryotic microorganisms; classification and diversity | 7 | |
| Cell structure: membranes, walls, endospores, organelles | 7 | |
| Fermentation and anaerobic respiration | 7 | |
| Bacterial growth: specific growth rate, doubling time, Monod model | 7 | |
| Pathogens, transmission routes and indicator organisms | 7 | |
| Cell chemistry: proteins, nucleic acids, lipids, polysaccharides | 6 | |
| Microorganisms in wastewater treatment and bioremediation | 4 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
Which method reveals the functional genes, not just the identities, of an uncultured soil community?
A. Shotgun metagenomic sequencing
Metagenomics sequences all DNA, revealing genes and pathways; 16S amplicons mainly identify taxa; staining and plating miss most organisms.
Further reading: See the manual sources: Brock Biology of Microorganisms; Pepper et al.; Rittmann & McCarty; Standard Methods Part 9000; WHO guidelines
Which organism forms endospores and is used as an indicator of remote or intermittent faecal contamination?
C. Clostridium perfringens
Its spores survive long in water, indicating past contamination and protozoan removal efficiency.
Further reading: See the manual sources: Brock Biology of Microorganisms; Pepper et al.; Rittmann & McCarty; Standard Methods Part 9000; WHO guidelines
Prokaryotic ribosomes are
A. 70S
Prokaryotes have 70S ribosomes; eukaryotic cytoplasmic ribosomes are 80S.
Further reading: See the manual sources: Brock Biology of Microorganisms; Pepper et al.; Rittmann & McCarty; Standard Methods Part 9000; WHO guidelines
Which bacterium oxidises ferrous iron and contributes to acid mine drainage and bioleaching?
A. Acidithiobacillus ferrooxidans
A. ferrooxidans oxidises Fe²⁺ and sulphides at low pH.
Further reading: See the manual sources: Brock Biology of Microorganisms; Pepper et al.; Rittmann & McCarty; Standard Methods Part 9000; WHO guidelines
How does a competitive inhibitor affect Km and Vmax?
D. Km rises; Vmax is unchanged
Competitive inhibitors compete for the active site and can be overcome by more substrate; non-competitive inhibitors lower Vmax.
Further reading: See the manual sources: Brock Biology of Microorganisms; Pepper et al.; Rittmann & McCarty; Standard Methods Part 9000; WHO guidelines
According to the Chick–Watson model, ln(N/N0) = −kCⁿt with n = 1, what happens to the required contact time if the disinfectant concentration is doubled?
B. It halves
With n = 1, inactivation depends on the product Ct, so doubling C halves t.
Further reading: See the manual sources: Brock Biology of Microorganisms; Pepper et al.; Rittmann & McCarty; Standard Methods Part 9000; WHO guidelines
Draining coastal sulphidic soils can create acid sulphate soils because
A. exposed sulphides oxidise to sulphuric acid
Oxidation of pyrite and other sulphides produces sulphuric acid, sharply lowering pH.
Further reading: See the manual sources: Brock Biology of Microorganisms; Pepper et al.; Rittmann & McCarty; Standard Methods Part 9000; WHO guidelines
Nitrification inhibitors such as dicyandiamide and nitrapyrin act by slowing
B. the oxidation of ammonium to nitrite
They inhibit ammonia monooxygenase, keeping nitrogen as ammonium and reducing nitrate leaching and N2O.
Further reading: See the manual sources: Brock Biology of Microorganisms; Pepper et al.; Rittmann & McCarty; Standard Methods Part 9000; WHO guidelines
Which bacterium is spread by inhaling aerosols from cooling towers and hot-water systems?
D. Legionella pneumophila
Legionella causes Legionnaires' disease via aerosols, not ingestion.
Further reading: See the manual sources: Brock Biology of Microorganisms; Pepper et al.; Rittmann & McCarty; Standard Methods Part 9000; WHO guidelines
On m-Endo medium in membrane filtration, total coliform colonies typically appear
D. red with a green metallic sheen
Total coliforms show a metallic sheen on m-Endo at 35 °C; faecal coliforms are blue on m-FC at 44.5 °C.
Further reading: See the manual sources: Brock Biology of Microorganisms; Pepper et al.; Rittmann & McCarty; Standard Methods Part 9000; WHO guidelines
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